Sphagnum response to nitrogen deposition and nitrogen saturation – a meta-analysis

Abstract Background: Sphagnum plants are sensitive to nitrogen deposition changes. However, previous literature is inconclusive on the response of Sphagnum species to nitrogen deposition, little is known about the nitrogen saturation of Sphagnum growth, and the effects of climatic, spatial and fertilization variables on the response of Sphagnum plants are still unclear.Methods: We conducted a meta-analysis of 66 experiments on nitrogen application to Sphagnum plants. The combined effect size of a random-effects model was used to analyze the effect of nitrogen deposition on Sphagnum growth. A mixed-effects model was established to determine the significance of each factor for the response of Sphagnum plants to nitrogen deposition. The nitrogen saturation value for Sphagnum species was obtained by fitting the regression function.Results: Sphagnum growth is promoted by moderate nitrogen deposition, and when nitrogen deposition exceeds the saturation value, Sphagnum growth is inhibited. The current nitrogen deposition saturation value for Sphagnum species is 19.34 kg ha-2 yr-1 globally and varies in different latitudinal zones. When Sphagnum plants are affected by excessive nitrogen deposition, low-water-table microhabitats and excessive temperature and precipitation can all exacerbate Sphagnum growth inhibition.Conclusions: Excessive nitrogen deposition will inhibit Sphagnum growth, and the nitrogen saturation values we obtained for Sphagnum species can be used to adjust fertilizer applications to protect Sphagnum plants from excessive chemical fertilizer application.